From: Mattias Jacobsson 2pi@mok.nu
[ Upstream commit 090158555ff8d194a98616034100b16697dd80d0 ]
Upon success the update_status handler returns a positive number corresponding to the number of bytes transferred by usb_control_msg. However the return code of the update_status handler should indicate if an error occurred(negative) or how many bytes of the user's input to sysfs that was consumed. Return code zero indicates all bytes were consumed.
The bug can for example result in the update_status handler being called twice, the second time with only the "unconsumed" part of the user's input to sysfs. Effectively setting an incorrect brightness.
Change the update_status handler to return zero for all successful transactions and forward usb_control_msg's error code upon failure.
Signed-off-by: Mattias Jacobsson 2pi@mok.nu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/usb/misc/appledisplay.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c index 993f4da065c3a..dabd1077d03c4 100644 --- a/drivers/usb/misc/appledisplay.c +++ b/drivers/usb/misc/appledisplay.c @@ -161,8 +161,11 @@ static int appledisplay_bl_update_status(struct backlight_device *bd) pdata->msgdata, 2, ACD_USB_TIMEOUT); mutex_unlock(&pdata->sysfslock); - - return retval; + + if (retval < 0) + return retval; + else + return 0; }
static int appledisplay_bl_get_brightness(struct backlight_device *bd)